SUPERWIND MODELS FOR THE DUST SHELLS AROUND INFRARED CARBON STARS

We investigate the observational effect of a superwind mass-loss phase driven by a thermal pulse in the interior of infrared carbon stars. W e modify the dust density distribution by adding dust to form a region of enhanced density which proceeds outward. Depending on the position and the degree of the enhancement, the emergent model spectral energy distributions can be significantly different from those with conventi onal power-law density distributions. These new results fit the observ ations of some infrared carbon stars better. In particular, the defici ency in 30-100 mu m observed fluxes of many infrared carbon stars, com pared with conventional model results, can be explained by the superwi nd models with standard dust grains. Our superwind models also cover a much wider range in observed IRAS 12-, 25- and 60-mu m colours than i s possible with conventional models. The time evolution of the spectra l energy distribution after a superwind can explain some observations of infrared carbon stars. We find that most of the observed infrared c arbon stars are in the early history of our superwind model. This may be due to a gradual increase in the mass-loss rate on the AGE or to th e selection effect of infrared carbon stars identified by the 11-mu m SiC feature.